Anhydrides

Reactions of anhydrides are analogous to those of acid chlorides.  They undergo hydrolysis, alcoholysis, and aminolysis in the same manner as acid chlorides except that they produce an acetate leaving group instead of a chloride ion.

In general anhydrides are most often utilized to perform acylations of alcohols or amines.  An acylation adds an acyl group.

Acetylation

For example, we could do an acetylation (an acylation with acetic anhydride that adds an acetyl group) of salicylic acid to form acetylsalicylic acid (aspirin).

Both acetic anhydride and benzoic anhydride are commercially available and used for acylations.

In this example, aniline is acylated with benzoic anhydride to form an amide.

Example Reactions

Acidic Hydrolysis

Basic Hydrolysis

Alcoholysis

Aminolysis